Ctrls performance

[JPRichings]

Initial pass on performance changed to remove thrust device_vector that is used to move ctrls to device that is causing a performance impact due to the thrust device_vector moving data from host to device on construction.

[JPRichings]

Todo:

• Confirm no horrible race condition is introduced by cudamemcpyToSymbol
• Set the ctrls buffer size programmatically or to some sensible limit, say 50? (at least 64KB of constant memory on device so no worries giving ourselves some extra room
• Apply fix to all kernels in QuEST

Assumptions in this code:

• Single operation on quantum register at a time which allows the assumption that ctrls can be overwritten before each subsequent gate application.

[otbrown]

Alloc size 64 qubits -- add as macro somewhere if not done already MAX_QUREG_SIZE

[TysonRayJones]

TODO: use a MAX_NUM_QUBITS = 64 or something constant in constants.hpp

[TysonRayJones]

Reminder of other stuff from meeting:

• storing targets also in constant mem
• retain passing ptrs to kernels; dispatcher passes constant mem ptr